Implementing a PLC-based temperature controller with PID algorithm
Author: Seyedreza Fattahzadeh – copyright 2014-
Binding: E-book in PDF format would be shipped on a CD ROM
Format: PDF file
Number of pages: 122
ISBN: 978-0-9839005-7- 3
PID controllers are used in most automatic process control applications in industry nowadays. PID controllers can be used to regulate flow, temperature, pressure, level, and many other industrial process variables. In this text I have specified guide lines to design and implement a temperature controller system using a mid range SIMATIC S7-300 PLC with PID algorithm. In text based on a defined project specification, we shall see how a SIMATIC S7-300 PLC hardware and its related developed control programs could be designed to implement a temperature control system that uses a close loop process control to maintain the temperature of a dyeing machine tank based on 4 typical predefined time temperature tables imbedded in the main program ready to be used by the operator by he can edit the data related to each function programs F1, F2, F3 or F4 depending on his particular application. The main function of the project is to maintain a set point from 25°C to 100°C. In this case, since temperature varies with time, the temperature is the dynamic variable, which is also called the process variable (PV). See Figure 3. To ensure the operation of the controller by the system operator is easy, two other application programs are developed to establish communication between two types of HMI devices: a typical HMI panel can be installed in a remote location, and a PC-based one. Hence the main control program is developed such to communicate with a typical HMI device. In this case, the operator can either use the HMI device or his PC’s monitor to check the closed looped system parameters (such as SP, PV (duration of time since system is started), change the operation of the system from Automatic to Manual or vice versa, or change/edit content of each time temperature tables etc. Also, as nowadays we see that all vital information are password protected in computerized system, this issue is also taken care of in developing the main circuit program in which an operator can not get any chance to edit any system parameter (gain, Ti, Td or any parameters related to the system) unless he is authorized and is given an access code. See figures 4 and 5 and 6. In application of both a pc based and a regular HMI device, the operator can view SV and PV values in real time when the system is executing the PID program and in case of a PC’s monitor, he can even view both values with respect to the time of a process. See figure 7. A typical dyeing machine temperature controller, controls the temperature of a dyeing trough based on a typical Time/Temperature curve. In which, it takes the controller about 140 minutes from start of process to end and it needs to follow the given cure to control the temperature of water in a dyeing though. Controller continuously calculates SV (set value), compares it with PV (sensor value) and turns output solenoid valve on or off to control the temperature.
Table of content:
Chapter 1, Abstract, PLC control method, Process control basics, What is the definition of a ‘PID control’?, A typical PLC control method, Application of a typical PanelMaster graphical display, Defining project specification and solution, Operating the system in automatic mode, Design and implementation of the controller’s hardware, Developing the main control software and HMI programs and data settings,
Chapter 2 , explanation of the main control program, Human Machine Interface (HMI) device, Steps to take to design a HMI application program, How to use PID.MCP; a WinCC-based application software, Question and answers related to this project, Conclusion, Appendix A: Slope of a straight line, Appendix B: What is the meaning of the block diagram, How does a PID loop work?, Tuning Parameters, Proportional Response, an analog multiplier circuit, Integral Response, an integrator circuit, Rectangular Rule, Trapezoidal Rule, Derivative Response, the Geometrical concept of the Derivative, Example 1: Finding energy from power, The Geometrical concept of the Derivative, Instantaneous induced voltage, The physical way or rate of change concept of the Derivative. Appendix C: The User Program, different block types and their application in SIMATIC STEP7 software.